Aromatase is the enzyme that converts androgen to estrogen. The applicant has hypothesized and demonstrated that aromatase is an important target of endocrine disrupting chemicals. These compounds have been found to inhibit aromatase activity, which results in both a decrease in the level of estrogen and an increase in the level of androgen in treated cells. Animal experiments have been performed that demonstrated the in vivo action of anti-aromatase chemicals. Additionally, environmental chemicals (both phytochemicals and xenochemicals) were found to modify the expression of aromatase in various tissues, which results in a change in the conversion ratio of androgen to estrogen. The compounds that inhibit aromatase or suppress aromatase expression behave as antiestrogens or androgen-like compounds in vivo. Conversely, compounds that either increase aromatase expression or enhance aromatase activity (or stability) may actually function as anti-androgens or estrogen-like compounds. Research conducted in the applicant's laboratory during the last four years demonstrated that estrogen-related receptor alpha (ERR-alpha) and estrogen receptor alpha (ER-alpha) can regulate the expression of aromatase. It has also been shown that endocrine disrupting chemicals, by acting as the ligands of these two receptors, can modify the expression of aromatase in treated cells. Aromatase, ER-alpha, and ERR-alpha are all important players in maintaining our endocrine function. To continue with and expand on the current efforts in the applicant's laboratory to identify endocrine disrupting chemicals, it is proposed in this competitive renewal application that they utilize their newly established high throughput computer-assisted virtual screening approach to search endocrine disrupting chemicals which serve as ligands/inhibitors of these proteins. It is also further proposed that they determine the structural characteristics of these chemicals by evaluating their structure activity relationship. Such structural information will be valuable for the identification of unanticipated endocrine disrupting chemicals. The proposed studies will focus on 1014 phytochemicals (including chalcones, chromones, coumarins, flavanones, flavones and isoflavones) that would be purchased from Indofine Co (Somerville, New Jersey). In addition, it is proposed that the endocrine disrupting actions of compounds (which have been identified by the high throughput screening method) be confirmed through both in vitro and in vivo experiments.